For John Krasinski, starring in his first romantic comedy seemed like just another day at, well, The Office. Director Ken Kwapis (The Sisterhood of the Traveling Pants), an Office vet who helmed the show’s pilot and the upcoming two-part season finale, championed Krasinski for the role of the affable groom-to-be who is forced by his fiancée (Mandy Moore) to enroll in a torturous marriage-prep class with her flaky family minister (Robin Williams). And three of Dunder Mifflin’s finest — Angela Kinsey, Brian Baumgartner, and Mindy Kaling — pop up in supporting roles. ”I was totally nervous,” Krasinski says of making the leap from TV to movies, but ”seeing them was like having a family visit.” The frequent ”Angela,” ”Kevin,” and ”Kelly” sightings thrilled even the film’s stars. ”Oooh, what Office cast members are coming to set today?” Moore remembers wondering. ”I think they were slightly horrified that I was as big a fan as I claimed to be.”

Krasinski had a similar crush on Williams, whom he grew up idolizing outside of Boston. And the Meet the Parents-style comedy called for him to go head-to-head with the old-school stand-up legend in a series of increasingly outrageous marital antibliss tests. ”Robin is not at all competitive about who’s the funniest guy in the room, because there’s no contest there,” says Krasinski. ”But there’s this one scene where we’re playing catch and I did this physical take, and totally as an aside he was like, blah, blah, blah, ‘…and that was the funniest thing I’ve seen on film.’ And I think my heart stopped for about five seconds when I heard him say that.”

Williams’ spontaneity meshed well with a gang accustomed to improvisation (Rachael Harris, alum of The Daily Show and the Christopher Guest films, also appears), and there were other unmistakable staples of Office life. Says Kwapis, ”For one millisecond in the film, and I won’t say where, John does look into the camera.” (July 4)